1. Field of the Invention
This invention relates to polyamides. In one aspect, the invention realtes to a process for manufacturing polyamides from an .alpha.,.omega.-dinitrile and an .alpha.,.omega.-diamine while in another aspect, the invention relates to a process utilizing a mixture of an oxygenated phosphorus compound and a molybdenum compound as a catalyst. In still another aspect, the invention relates to an improved process for manufacturing nylon-6,6 from adiponitrile and hexamethylene diamine utilizing a catalyst system composed of a mixture of an oxygenated phosphorus compound and a molybdenum compound.
2. Description of the Prior Art
The art is replete with references describing various methods for preparing commercially available nylons from diamines and dicarboxylic acids. The art also contains teachings for preparing nylons from diamines and dinitriles. For example, U.S. Pat. No. 2,245,129 by Greenwalt describes a method for producing a linear polyamide by heating a reaction mixture of a dinitrile, a diamine and water. The procedure consists of two stages. In the first stage the reaction mixture is heated in a closed reaction vessel until a low molecular weight polyamide is formed while in the second stage, this low molecular weight polyamide is converted to a high molecular weight polyamide upon additional heating.
U.S. Pat. No. 3,847,876 by Onsager teaches another method for preparing a high molecular weight polyamide comprising contacting a dinitrile, a diamine and water. The Onsager process requires at least equal molar amounts of diamine and dinitrile to be initially present in the reaction mixture and further requires that the polymerization occur in the presence of controlled amounts of ammonia, preferably in the presence of at least three weight percent based on the total weight of the diamine, dinitrile and water. This generally entails addition of ammonia to the reaction mixture over the course of the reaction.
Recently Hoffmann et al., U.S. Pat. No. 4,436,895, disclose an improved method for preparing a high molecular weight polyamide from a dinitrile, diamine and water by conducting the polymerization in the presence of an oxygenated phosphorus compound, such as phosphoric acid, or an ammonium or ammonium alkyl salt of the acid. This process reduces the conventional reaction time of the polymerization and produces a high molecular weight, linear polyamide having desirable weight loss spinning properties.
Recently Coffey et al, U.S. Application Ser. No. 540,596 filed Oct. 11, 1983, now U.S. Pat. No. 4,490,521, disclose a method for the improvement of resin thermal stability through the use of metal salts of oxyphosphorus acids, such as disodium phosphite, as the catalyst.
While all of the above methods and others known in the art demonstrate utility for manufacturing linear polyamides, the nylon fiber industry continues to seek manufacturing improvements which result in superior quality polyamide. Of particular interest are process improvements which will result not only in reduced operation cost and the corresponding increase in operation efficiency, but which will also result in a spinnable polyamide that will have superior weight loss properties.